# std::filesystem::directory_entry::file_size

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< cpp‎ | filesystem‎ | directory entry

std::uintmax_t file_size() const; | (1) | (since C++17)
std::uintmax_t file_size( std::error_code& ec ) const noexcept; | (2) | (since C++17)

If the file size is cached in this `directory_entry`, returns the cached value. Otherwise, returns:

1) std::filesystem::file_size(path()),
2) std::filesystem::file_size(path(), ec).

### Parameters

ec | - | out-parameter for error reporting in the non-throwing overload

### Return value

The size of the referred-to filesystem object.

### Exceptions

Any overload not marked `noexcept` may throw std::bad_alloc if memory allocation fails.

1) Throws std::filesystem::filesystem_error on underlying OS API errors, constructed with p as the first path argument and the OS error code as the error code argument.
2) Sets a std::error_code& parameter to the OS API error code if an OS API call fails, and executes ec.`clear`() if no errors occur.

### Example

Prints the list of files in a given directory alongside with their sizes in human readable form.

Run this code

    #include <cmath>
    #include <cstdint>
    #include <filesystem>
    #include <iostream>

    struct HumanReadable
    {
        std::uintmax_t size{};

        template<typename Os> friend Os& operator<<(Os& os, HumanReadable hr)
        {
            int i{};
            double mantissa = hr.size;
            for (; mantissa >= 1024.0; mantissa /= 1024.0, ++i)
            {}
            os << std::ceil(mantissa * 10.0) / 10.0 << i["BKMGTPE"];
            return i ? os << "B (" << hr.size << ')' : os;
        }
    };

    int main(int argc, const char* argv[])
    {
        const auto dir = argc == 2 ? std::filesystem::path{argv[1]}
                                   : std::filesystem::current_path();

        for (std::filesystem::directory_entry const& entry :
             std::filesystem::directory_iterator(dir))
            if (entry.is_regular_file())
                std::cout << entry.path().filename() << " size: "
                          << HumanReadable{entry.file_size()} << '\n';
    }

Possible output:

    "boost_1_73_0.tar.bz2" size: 104.2MB (109247910)
    "CppCon 2018 - Jon Kalb “Copy Elision”.mp4" size: 15.7MB (16411990)
    "cppreference-doc-20190607.tar.xz" size: 6.3MB (6531336)
    "hana.hpp" size: 6.7KB (6807)

### See also

file_size (C++17) | returns the size of a file (function)

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